1. Field of the Invention
The invention relates to an unscrewing mechanism in an injection molding apparatus for forming threaded molded articles such as caps.
2. Description of Related Art
Methods, and in particular, apparatus or mechanisms for forming threaded molded articles in an injection molding operations are known in the art.
Known related art includes the apparatus depicted in U.S. Pat. No. 5,776,521 to Wright et al. This patent discloses a method of ejecting the molded part by rotating the ejector sleeve as it follows the part up and off the core. Other methods or devices are depicted in U.S. Pat. Nos. 2,558,027 and 2,799,049 to Wilson. The former Wilson patent discloses the use of adjustable spring pressure for the movement of the stripper plate. The molded thread is what gages the stripper plate movement as it is unscrewed. The latter Wilson patent discloses a method of anti-rotation designed by sinking the product head with ratchet teeth on the outside diameter into the stripper plate side and uses the adjustable spring pressure technology disclosed in the former patent to activate the stripper plate.
Other known related methods and mechanisms for making molded threaded articles include U.S. Pat. No. 5,518,679 to Junk, U.S. Pat. No. 5,061,168 to Fox, and U.S. Pat. No. 4,767,587 to Town.
Many of the prior art devices have inherent problems such as complexity, cooling problems associated with the inherent design, wear problems to bushings and seals due to the design of the mechanisms, and similar problems associated with the inherent complex designs of such mechanisms.
For example, as shown in prior art drawing FIGS. 1a and 1b, the cooling of plastic is done faster through the use of a non-elevating or laterally rotating core 2. Water bubblers can maintain optimum space 1 at the internal tip of the core to maximize cooling. There is no movable stripper plate or stripper plate action as contemplated by the present invention. An object of the present invention would provide an unscrewing core that rotates but remains in position such that a water bubbler can maintain an optimum space 1 at the internal tip of the core 2.
Another example of current practice is unscrewing the core from the plastic cap into a threaded chase. This requires the core to move laterally as it rotates following the thread pitch being molded. The core""s alignment is by means of metallic bearing material (bronze) in a friction condition. The present invention reduces wear with the use of ball or roller bearings on a stationary rotating core.
FIGS. 1c and 1d again depict another prior art configuration with an inner core wherein the outer thread shell backs out of a stripper ring; there is no stripper plate action; the inner core 3 is stationary; and there is no cooling the threaded core shell 2.
The present invention also saves cycle time. As the mold opens, the core and striper plate will move in unison for part ejection, a process which may be called ejection on the fly. In addition, fewer manufactured components are needed in the cavity stack for the present invention thereby providing a simplified assembly with reduced maintenance requirements.
The present invention is an unscrewing mechanism for forming threaded components comprising at least one rotatable elongate mold core which has a threaded portion at one end for molding one of an external thread, an internal thread and a combination thereof for a threaded component to be formed. Also included is a mating mold surrounding a portion of each of the at least one rotatable elongate mold core including the threaded portion when in a mold closed condition therein defining a mold cavity between said at least one rotatable elongate mold core and said mating mold into which molten material is injected to form the threaded component.
The mating mold is a portion of a cavity plate and independently movable relative to said at least one rotatable elongate mold core to a mold open condition when said mating mold is spaced from the at least one rotatable elongate mold core.
A stripper plate is provided in overlying relationship to a stationary plate. The stripper plate is movable and separable from the stationary plate in a direction parallel to an axial direction of the at least one rotatable elongate mold core for ejecting the formed threaded component when in the mold open condition, the stripper plate further being in underlying relationship to said cavity plate when in the mold closed condition.
Means for moving the stripper plate in the direction parallel to the axial direction of the at least one rotatable elongate mold core is provided, the means further being for rotating the at least one rotatable elongate mold core such that a movement of the stripper plate to eject the formed threaded component is at the same rate as the unscrewing of the at least one rotatable elongate mold core threaded portion.
The means for moving the stripper plate includes jack screw means, the jack screw means being threaded and metered so that the stripper plate is moved to eject the formed threaded component at the same rate that the threaded portion of the at least one rotatable elongate mold core unscrews. The jack screw means comprises a riser component, the riser component being in a slidable relationship with the stationary plate; and means for preventing the riser component from rotating as it moves the stripper plate away from the stationary plate and as it moves to allow the stripper plate to return for molding another threaded component.
The means for preventing the riser component from rotating comprises at least one flat portion along its outside perimeter, the flat portion being juxtaposed a mating flat portion in the stationary plate.
In another embodiment, the jack screw means comprises a riser component; a riser chase component surrounding said riser component, said riser component being in a slidable relationship with the riser chase component, the riser chase component being fixed thereto; and means for preventing the riser component from rotating as it moves the stripper plate away from the stationary plate to for ejecting the formed threaded component and as it moves to allow the stripper plate to return for molding another threaded component. In this embodiment, the means for preventing the riser component from rotating comprises at least one flat portion along its outside perimeter, the flat portion being juxtaposed a mating flat portion in the riser chase component.
The unscrewing mechanism for forming threaded components further comprising a fixed core cooling plate; and a bottom bearing plate in overlying relationship to the fixed core cooling plate and fastened to said fixed core cooling plate. The stationary plate is in overlying relationship to the bottom bearing plate and fastened to said bottom bearing plate; and the at least one rotatable elongate mold core is disposed on the fixed core cooling plate at one end and extends therefrom through an aperture in each of the bottom bearing plate, the stationary plate and the stripper plate such that the threaded portion extends beyond an upper surface of the stripper plate when said stripper plate is in condition for molding another threaded component and the threaded portion engages the mating mold in the cavity plate so as to define the mold cavity.
Bearing means in each of the stationary plate and bottom bearing plate through which the at least one rotatable elongate mold core extends is provided for facilitating a rotating action of the at least one rotatable elongate mold core in a clockwise and counter-clockwise rotation.
The at least one rotatable elongate mold core further comprises longitudinal gear teeth around a perimeter of an intermediate portion of said at least one rotatable elongate mold core.
The means for moving the stripper plate further includes an elongate drive gear, which is parallel to the at least one rotatable elongate mold core. The elongate drive gear has longitudinal gear teeth around a perimeter of an intermediate portion of said elongate drive gear. The longitudinal gear teeth of the elongate drive gear are in cooperative gear teeth mesh engagement with the mating longitudinal gear teeth of the at least one rotatable elongate mold core. Also provided is means for driving the elongate drive gear so as to cause clockwise and counter-clockwise rotation such that when the elongate drive gear is made to rotate clockwise, the at least one rotatable elongate mold core rotates counter-clockwise, and when the elongate drive gear is made to rotate counter-clockwise, the at least one rotatable elongate mold core rotates clockwise.